NEW YORK (Reuters Health) - Appendectomy is associated with an increased risk of Parkinson's disease (PD), according to a large observational study.

Aggregated alpha synuclein, a pathologic feature of PD, is found in the brain and the gastrointestinal (GI) tract, and the accumulation in the GI tract is believed to occur first, suggesting that the gut may have a role in development of the neurodegenerative disease, Dr. Gregory Cooper of Case Western Reserve University in Cleveland, Ohio, explained at a press briefing May 8, ahead of study presentation at Digestive Disease Week (DDW) later this month in San Diego, California.

"It's thought that potentially this protein is released from damaged nerves in the gut, then transported to the brain," he said. But there are conflicting reports on whether appendectomy increases the risk of PD, Dr. Cooper added.

He and colleagues analyzed electronic health records from 26 U.S. healthcare systems representing more than 62 million patients.

Among more than 488,000 patients who had their appendix removed, 4,470 (0.92%) developed PD at least six months later. Of the remaining patients who did not have appendectomy, 0.29% developed the disease.

The overall relative risk of developing PD was 3.19 (95% confidence interval, 3.10 to 3.28; P<0.0001) in patients who had appendectomy compared with those that did not.

"This research shows a clear relationship between the appendix, or appendix removal, and Parkinson's disease, but it is only an association. Additional research is needed to confirm this connection and to better understand the mechanisms involved," lead author Dr. Mohammed Sheriff said in a conference news release.

Dr. Mahyar Etminan from the departments of ophthalmology and neurology at the University of British Columbia, in Vancouver, Canada, who was not involved in the research, also urged caution in drawing any firm conclusions.

In an email to Reuters Health, he noted that the six-month "risk window for PD diagnosis is inadequate. PD can take up to 10 years to develop so it is possible that at least some of the PD cases may not have been attributed to appendectomies."

There is also a possibility of selection bias if the group without appendectomies were not followed as long as the appendectomy group (i.e., were lost to follow-up or died before developing PD). "This selection bias might have contributed to the larger risk ratio for the appendectomy group," Dr. Etminan said.